When a pair of genes is required to produce a certain trait (such as pied), and only one gene is present, the snake is "het" for that trait. It CAN be something other than "normal" looking though. A pastel bp is "het for super-pastel"...but since we can look at the snake and SEE that it's a pastel, we don't usually call it a het.

When a snake is referred to as a "possible het" that means at least one parent or grandparent in its lineage carried the gene being referred to, but there is no way to tell if the normal-looking snake inherited that gene or not.